Production of aromatic carboxylic dianhydrides with vanadium containing catalysts



United States Patent Int. c1. (30% 63/00 US. Cl. 260--346.3 3 Claims ABSTRACT OF THE DISCLOSURE Process for the production of aromatic carboxylic dianhydrides by the catalytic dehydro-oxidation of adducts of diene hydrocarbons and maleic anhydride in which the dehydro-oxidation is carried out in the gas phase in the presence of a vanadium containing catalyst.

This invention relates to a process for the production of aromatic carboxylic acids.

It is known to convert adducts of diene hydrocarbons and maleic anhydride obtained by Diels-Alder synthesis into aromatic carboxylic acids by dehydrogenation and oxidation. For example, it is possible to condense isoprene with maleic anhydride and dehydrogenate the resultant methyl-A -tetrahydrophthalic anhydride by means of sulfur. The 4-methylphthalic anhydride thus obtained can be converted into trimellitic acid with potassium permanganate.

When carrying out the process described above for the production of aromatic carboxylic acids on a commercial scale, one will endeavor among other things to carry out the dehydrogenation and oxidation of the diene adducts economically and, if possible, to combine both reaction steps in one process stage.

The direct oxidation of the diene adducts in liquid phase with nitric acid or potassium permanganate proceeds with ring cleavage and leads to the formation of aliphatic polycarboxylic acids. For example, A -tetrahydrophthalic anhydride obtainable by condensation of butadiene and maleic anhydride gives butane tetracarboxylic acid-1,2,3,4 when treated with the oxidizing agents mentioned above.

Another difficulty is due to the fact that the adducts prepared by diene synthesis may be cleaved to form again the starting substances in case of an increase in temperature. This cleavage giving again the starting products may sometimes reach a considerable extent already at relatively low temperatures.

Attempts heretofore made to prepare aromatic carboxylic acids by direct simultaneous dehydrogenation and oxidation of alkyl substituents of diene adducts with satisfactory conversion rates and yields were unsuccessful. The diene adducts have rather been converted first into stable aromatic compounds by dehydrogenation and the latter oxidized to form aromatic carboxylic acids.

It has now been found that adducts of diene hydrocarbons and maleic anhydride may be converted into aromatic carboxylic acids by simultaneous dehydrogenaice tion and oxidation when operating by the process of the invention which is characterized in that the diene adducts used as the starting materials are simultaneously dehydrogenated and oxidized with oxygen or oxygen-containing gases in the gaseous phase over solid vanadiumcontaining catalysts which are known per se and which advantageously contain further metals or compounds thereof.

These catalysts are already used for the oxidation 01 aromatic hydrocarbons to form aromatic carboxylic acids e.g. for the oxidation of o-xylene to form phthalic anhydride or for the oxidation of durene to form pyromellitic anhydride. They consist of refractory inert carriers such as, for example, pumice, gravel, quartz, A1 0 or preferably SiC coated with a layer of the catalytically active material. The catalytically active coating consists of V 0, alone or of V 0 and additions of other metals or metai catalysts comprising 6090% by weight of V 0 and 10-40% by weight of TiO SnO W0 or A1 0 The simultaneous dehydrogenation and oxidation ir accordance with the invention of the diene adducts ir the gaseous phase with the catalysts proposed may be effected with air in tubular reactors, e.g. those used f0] the oxidation of o-xylene to form phthalic anhydride The air is preferably preheated to ISO-300 C. and the supply rate, i.e. the ratio of air to catalyst volume, i: preferably within the range of from 2.0 to 3.5 norma cu. m. of air per liter of catalyst per hour and the loac is desirably 10 to 35 g. of feed product per normal cu. m of air. The temperature of the salt bath of the tubula1 reactors ranges between 360 and 480 C. and preferably between 380 and 400 C.

The process of the invention is particularly suitable f0] the production of aromatic polycarboxylic acids. F01 example, hexadiene-2,4 may be condensed with maleit anhydride to form 3,6-dimethyl-A -tetrahydrophthali anhydride and, by the simultaneous dehydrogenation ant oxidation in accordance with the invention, converter into prehnitic anhydride in one process step.

The process of the invention is applicable with par ticular advantage to the production of pyromellitic dian hydride. The starting material used in this case is 2,3-di methyl butadiene-1,3 which is readily obtainable by dimerization of propene and which is condensed witl malic anhydride according to Diels-Alder. As describe in the example, the resultant 4,S-dimethyl-M-tetrahydro phthalic anhydride is converted into pyromellitic dian hydride by simultaneous dehydrogenation and oxidation EXAMPLE 160 g. of a mixture of by weight of V 0 am 25% by weight of Ti0 were fused at 700-900" C. 01 1 liter of gravel having a particle size of 23 mm.

The catalyst thus obtained was charged to the reactiol tube of a salt bath furnace. The tube had a diameter 0 44 mm. and was filled to a height of 1 m.

4,5-dimethyl-A -tetrahydrophthalic anhydride preheate to C. was charged to the furnace at a temperature 0 the fused salt bath of 400 C. The feed was charged a a rate of 20.8 g. per normal cu. m. of air and the air wa supplied at a rate of 2.5 normal cu. m. of air per hou per liter of catalyst.

Pyromellitic anhydride in a yield of 60% by weigh corresponding to 49.5% of the theoretical yield was re covered in the cooling devices downstream of the reactor.

What is claimed is:

1. In the dehydro-oxidation of adducts of alkyl substituted conjugated dienes containing from 6 to 12 carbon atoms and maleic anhydride to produce an aromatic carboxylic dianhydride, the improvement comprising effecting the dehydro-oxidation in a single reaction stage in the gas phase over a catalyst comprising in the range of 60 to 90 percent by weight of vanadium pentoxide and in the range of 10 to 40 percent of an oxide selected from the group consisting of TiO SnO W0 and A1 0 References Cited Sugasawa et aL, Chem. Abstracts, vol. 36, p. 92 (1941).

ALEX MAZEL, Primary Examiner B. I. DENTZ, Assistant Examiner P0405) UNITED STATES PATENT OFFICE 569 CERTIFICATE OF CORRECTION Pate 506,639 Dated pril 14, 1970 Inventor-(s) KARL PE-TERLEIN It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

F' Column 2, lirie 17 after "metal" insert --comp0u.nds preferably the oxides The catalytically active coating of these--; line 18 "comprising" should be --comprises- SIGNED AND SEALED AUG 4 4970 4 Atmt:

Edward M. Fletcher, Jr. m1 3. 33 511685115 officer commissioner 02 19am?! 

